I recommend you to enable the clone display configuration through the video driver console following the information on this URL:
Also make sure that the internal configuration of the TV is set to use the HDMI port as the input signal source.
Also try hot plugging the hdmi cable while the video driver console is opened, and try also resting the computer with the cable already connected and checking if you get any video signal while the system is posting.
In addition, update the BIOS of the computer, this will update the video BIOS of your computer. If possible try using another HDMI cable and port. Make sure to test this using the laptop connected to the AC power, not using the laptop's battery.
Furthermore, check with the laptop manufacturer and verify the the HDMI port on the computer is enabled and fully functional.